1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor by using a crystal growth apparatus in which a crystal growth is carried out by decomposing a source gas thermally on a wafer heated to reach a high temperature, especially by using a vertical MOVPE (Metal Organic Vapor Phase Epitaxy) apparatus of high speed revolution type.
2. Description of the Related Art
In the crystal growth using the MOVPE apparatus, the following document is disclosed as a method for improving an uniformity within a surface of a wafer of a growth layer: document “2001, International Conference on Indium Phosphide and Related Materials Post Deadline Papers pp.15-16. 13th IPRM 14-18, May 2001 Nara, Japan”.
Recently, since an epitaxial wafer, which is a wafer with a thin film layer grown thereon, is used in most electronic devices, a mass production technology of the epitaxial wafer is indispensable. VPE (Vapor Phase Epitaxy), MBE (Molecular Beam Epitaxy), MOVPE and so on are currently in practical use as an epitaxial growth technology.
In the epitaxial growth technology, the MOVPE to be described in the present invention is a method for growing a thin film crystal of chemical compound semiconductor on a wafer by reacting III-group organic metal with V-group gas on the heated wafer. In order to mass-produce by using this MOVPE, a multi-charge method to grow a plurality of crystals at the same time is indispensable, and one of the methods in practical use currently is the method of vertical and high speed revolution type. In this method of vertical and high speed revolution type, since the crystal is grown uniformly inside the wafer surface by charging the wafer surface and by flowing a reaction gas vertically, that is, in a longitudinal direction, a susceptor holding the wafer is made to revolve.
During crystal growth, however, the temperature distribution of the surface of the wafer in which the crystal is actually grown becomes different according to the thermal conduction of a wafer holder. And then, the following problems occur: the efficiency of a source gas decomposition on the surface of the wafer changes; the composition also changes sensitively; and the uniformity within the surface deteriorates due to the difference of composition distribution within the surface.
In the document mentioned above, using the change of band gap wavelength with the change of composition due to the temperature, and relating to a method for controlling wave length in the crystal growth using the MOVPE apparatus, there is disclosed a method for improving the uniformity by controlling the wavelength within the surface after improving controllability by controlling directly the change of temperature owing to the type of gas introduced and the change of flow rate.
In order to examine the temperature distribution within the surface of the wafer, a PL (Photo Luminescence) peak wavelength is actually measured when a four element mixed crystal of indium gallium arsenic phosphorous (InGaAsP) with the band gap wavelength of 1.3 micrometers is grown by the MOVPE apparatus. The PL is to measure an impurity level contained in the crystal by observing a light emitted from a semiconductor, changing the wavelength of light radiated to the semiconductor. In this case, a band gap wavelength distribution within the surface of the wafer can be obtained.
In this band gap wavelength distribution, that is, the composition distribution, the wavelength is long at the central part and shifts to be short as nearing the peripheral part of the wafer with the shape of concentric circle or almost the same shape. There can be recognized that the temperature distribution within the wafer surface becomes higher by approximately 3-4° C. as shifting from the central part to the peripheral part of the wafer, by inversely converting the wavelength distribution from the dependence on growth temperature of the band gap wavelength.